Electrical protective device



March 23 1926.`

' 1,577,719 W. H. T. HOLDEN ELECTRICAL PROTECTIVE DEVICE Original Filed Dec. 5o, 1922 IN VEN TOR C A TTORNEY Patented Mar. 23,. 1926.

UNITED STATES PATENT OFFICE.

WILLIAM H. T. HOLDEN, F BROOKLYN, NEW YORK, ASSIGNOB TO AMERICAN TELE- PHONE & TELEGRAPH COMPANY,

A CORPORATION OF NEW YORK.

y ELECTRICAL PROTECTIVE DEVICE.

Application led December 430, 1922, Serial No. 609,889. Renewed October 9, 1925.

To all lwhom t may concern Be it known that I, WILLIAM H. T. HOLDEN, a citizen of the United States, residing at Brooklyn, in the county of Kings and State of New York, have invented certain Improvements in Electrical Protective Devices, of which the following is a'v speciication.

This invention relates to electrical protective devices and particularly to means for protecting a radio signaling system from the effects of high potentials set up in the antenna circuit of such systems by causes usually arising from sources external to the signaling system itself.

In the operation of radio signaling sys-A tems, high potential surges or oscillations, which may be set up in such systems by static or lightning, are capable not only of producing serious effects upon the apparatus associated with the signaling circuit but also present a great hazard to the operator of suchcircuit. lSuch high, transient voltages may cause notvonlya. burn-out in some part of the'apparatus thatis unable to withstand the high voltage, but also severe injury to the station operator. l

It is the object of this invention to pro- .vide means for substantially eliminating the hazard to the operator as well' as the effect upon the physical structure of the radio circuit of high potential surges or oscillations set up in the antenna circuit by static, lightning or other causes.

This invention will be clearly understood from theI following description when read in connection with the attached drawing of which Figure 1 shows a radio signaling ciri' cuit with a thermionic protect-ive device associated therewith constituting one form of embodiment of the invention; Fig. 2 shows another formof embodiment of the invention, and Figs. 3 and 4 show two types of thermionic discharge devices which may be used in connection with the circuits shown in Figs. 1 and 2. j

lIn the ,circuit sho-wn in Fig. 1 the antennaA 1 has connected in series therewith to groundthe winding 2 o f the transformer 3, the other winding 4 of which is connected with a terminal circuit which may be adapted either to transmit br receive or to perform both of these functions 'The circuit manner of doin connected with winding 4 maybe of any well-known type of terminal circuit adapted to perform any or all ofthe functions A just mentioned. yA thermionic discharge, de-

vice 5 i s connected with the antenna 1 and 1s therem effectively bridged across the terminals of the antenna winding .2 of the' transformer 3. This thermionic device has a lnghly evacuated envelope 6 in which a plurality of electrodes are inserted and sealed so as to maintain a high degree of vacuum. The electrodes 7 and 8 are adapted to be heated by current from a source 17 of low frequency alternating current, the which will be later madek clear. As will e noticed, the filaments 7 and 8 are effectively connected with the terminals of the antenna winding 2. The cold electrodes or 'ds 9 and 10 are also effectively connecte with the corresponding terminals of the winding 2 to which the filaments 7 and 8 are connected. These grids are biasedv negatively by means of the bat` teries or equivalent sources of direct current 11 and 12. `The filament 7 is connected by the conductors 13 with one of the windings 144 of the transformer 15, the other winding 16 of which is connected with the i source of low frequency alternating current 17. Connected in series with the conductor 13 are the windings 23, 24, 25 and 26 of choke coils. The transformer 15 is preferably of the iron-core type designed toreadily` transmit low frequency currents but to offer higllihim edance to high frequency currents. eo ject of the choke coils designated 23 to 26 inclusive is to prevent high frequency currents from passlng through the transformer 15 by virtue of the capacity that may exist between'the windings of this transformer. ment 8 is connected by the conductors 18 with the winding 19 of the transformer 20, the other winding 21- of which is connected by the conductors 22with the source of low frequency current 17 The `magnitude of the filament heating current might be controlled by proper adjustment of the voltage of the source 17. or in other ways that will readily occur to one skilled in the art.

In the operation of the afore-described system embodying my invention', when the lmaximum signal voltage to be transmltted 1s In similar manner-.the fila#A les applied by the transformer 3 across the antenna winding 2, a space current would flow be-M tween the cathodes 7 and 8 if these cathodes were heated and no potential was applied to the grids. Since it is not desired to have the protective device operate within the limits y of the signaling voltage, the'grids 9`and 10 are biased negativelyby the direct current sources 11 and 12 in orderl to prevent the flow' of' any space current between the cathodes 7 and 8 when the voltage across the` terminals of the winding 2 is not greater than .the maximum signal voltage to be transmitted from the antenna 1. If, however, a high'voltage surge or oscillation is setup in the antenna 1 (and consequently in the winding 2), 'the magnitude of which is greater than the maximum signal voltage i that would beimpressed across the said winding 2, the potential between cathodes l7 and 8 would cause a flow of space current therebetween which would shunt the winding 2 of the transformer 3 and greatly minimize not only the electrical'stresse's that might be placed upon thephysical apparatus associated with the terminal circuit but would also greatly minimize the hazard to which the operator might thereby be subjected. When the voltage produced by the 'surge diminishes `to the value for which the grids would be suiciently negative to prevent the alent to two three-electrode devices.

' electrode 8 be negative, but also the grid 10 associated therewith will be negative.

that the electrodes S and 10 are, in effect, equivalent to a single electrode, and therefore under the assumed-condition the-thermionic device 5 is equivalent to a threeelectrode device. A similar condition exists l'when the point b is positive and a is negative. Under this condition the electrodes 7 and 9 would both be negative, and accordingly the device 5 would be equivalent to a three-electrode device.

While the arrangement shown in Fig. 2 differs structurally from thatshown in Fig. 1, it is in principle substantially the same as that shown in Fig. 1. The principal difference between the two arrangements resides .in the fact that in the circuit shown in Fig. 2 the filament heating current is derived from the source of high frequency oscillations whereas in the circuit of Fig. 1 this currentwas obtained from a source of low So 'y frequency Icurrent 17'. In the arrangementl 'l shown in Fig. 2, in which the same numerals have been used to represent; parts that are the same as in Fig. 1,'the transformer 3 has not only two main windings 2 and 4 which couple the terminal circuit to the antenna circuit, but also has auxiliary windings 29 and 30 which are connected. with the filaments 7 and 8 of the thermionic device 5. By means of these auxiliary windin s the required amount of current is obtaine from the high frequency source to heat the lilaments 7 and 8 inorder to produce the necessary electron emission therefrom. The

grids' 9 and 10 which are biased negatively by the sources 11 and 12 are connected with the filaments 7 and 8 respectively.` It will therefore be seen that the principle of operation of the circuit of Fig. 2 is substantially the same as that of Fig. 1 and furtherexplanation need therefore not be given. The arrangement of Fig. 2 is, however, considyered less desirable than that of Fig. 1 in view of the fact that it utilizes for the heating of the filaments the high frequency energy which as is well known is much more costly than the 60 cycle current such as would probably be used in the arrangement of Fig., 1.

Figs. 3 and 4 show two types of thermionic devices which may be used in the circuits of Figs. `1 and 2. .In both of the devices shown in Figs. 3 and 4 the envelope 6 is highly evacuated, 'so that the resultant action of either type of device is entirely electronic and not by virtue of any gas that might be contained therein. In the arr'an ement shown in Fig. 3 the cathodes 7 an 8 are inserted in the ends of the tube and adapted to be connected with the 4externa-l circuit by means of suitableleading-in wires.

the tube which therefore reduces the number of seals necessary and improves the construction generally.

While this invention has been shown as embodied in particular forms and arrangements of parts it is to be understood that it is not limited to the particular forms andarrangements shown but is capable of embodiment 1n other forms and arrangements withinthe spirit and scope of the appended claims. v

What'is claimed is: 1. In a radio signaling system, the combination with an antenna, of a terminal ciru-it., a Goulning I- transformer having anv antenna win g connected with the said antenna and a circuit winding'connected with the said terminalcircuit and a thermionic protective device bridged across the said antenna winding, the said protective device having an'evacuated` sealed envelope containing a cathode individual to and connected with eac-h terminal of the said antenna' winding, a grid individual to and connected lwith each terminal of the said anheating current with the said cathodes.

tenna winding, a source of Acurrent for heating said cathodes, a source of potential to negatively biaseach of the said grids with respect to thepnearer cathode andmeans to prevent the flow of antenna currents over the circuit lconnecting the said source of age through the said source of heating current.

3. In an electrical protective system," the' coi'nbination with acircuit to be protected against abnormal voltages, of a source of normal voltage connected therewith for transmission thereover, a thermionic protective device connected with the said circuit having a plurality of cathodes and a plurality of grids enclosed in an 'evacuated vessel, one of said cathodes'and one of said grids being connected with one side of said circuit, and another cathode and another v wgrid being connected with the other side of the said circuit, each grid being biased negatively to the nearer cathode, a source of current to heat the said cathodes, and means between the said source and one of Asaid cathodes to prevent the dissipation of energy from the source of normal voltage through the source of heating current.

4. In an electrical protective system, the combination with a circuit to bel protected against labnormal voltages, of a source of signaling potential connected therewith for transmission thereover, a, thermionic protective device connected with the said circuit having acathode and a grid enclosed in an evacuated vessel, a' source of current connected withthe said cathode to supply heating current thereto,`means to bias los negatively the said grid -to prevent the passage through the thermionic device of currents of the normal signaling potential, and

l supply negatively bias each of the said grids with Y means connected between said cathode-and the said source of heating current to prei vent the dissipation of energy from the sig-Y 'Y *i naling source through the said source of'.

heating current.' .Y

5. an electrical protective system, the

combination with a circuit to be protected against abnormal voltages, ofva source of 'signaling potential connectedk therewith,a

thermionic protective device having a plurality of cathodes and a pluralityof grids in an evacuated vessel, one of said cathodes and one of said grids being connected with one side of the said circuit, yanother cathode and'another grid being connected with the other side of the said circuit, a source of current connected with the said cathode to heating current thereto,v means to respect to the nearer cathode to prevent the passage through the thermionic device of normal signaling currents, and means connected between the said cathode and the said source of heating current to prevent the dissipation of energy from the said signaling source through the source of heating current.

6. ln a radio signaling system,` the combination lwith an antenna, of an impedance connected in series therewith, anda thermionic protective device bridged across the said impedance, said device having an evacuated sealed envelope containing a heated electrode individual to and connected with each terminal of the said impedance and a cold electrode likewise individual to and connected with each terminal, both cold elec# trodes being within thev space between the heated electrodes, and each cold electrode being negatively biased with respect to that heated electrode connected with the same terminal of said impedance to prevent the flow of spacecurrent between the said heated electrodes when the voltage across the said impelance does not exceed a certain critical va ue.

7. Ina radio signaling system, the combi- I nation with a grounded antenna, of a cou-- pling transformer having an antenna winding connected with ssd antenna and a circuit winding connected with a terminal circuit and a protective device also connected with the said antenna in parallel with the said antenna winding, the said protective device having an evacuated sealed envelope containing a heated electrode individual to and connected with each terminal of the said winding and a`cold electrode likewise individual to and connected with each terminal, both cold electrodes being within the space between the heated electrodes, and each cold electrode being negatively. biased with respect to that heated electrode connected y with the same terminal of said impedance to Vprevent the :How of space current between nac the saidlieated electrodeswlien 'the voltage; across the said antenna wlnding is less than cuit, acoupling transformer having an antenna winding connected with "the said antenna and a circuit winding connectedy with the said terminal circuit, anda thermlomc protecti ve device havingan evacuated Vsealed envelope containing a heated eleci trode individual to and connected with each terminal of the said antenna winding and .a cold electrode likewise individual to and connected with each terminal, both cold electrodes being within the space. between the heated electrodes, and each cold electrode being negatively biased with respect to that heated electrode connected with the same terminalto prevent, the flow of space current between the said heated electrodes when the voltage across the said antenna winding is less than a certain critical value.

9. In a radio signaling system, the combi i nation with an antenna, of a terminalcircult, 'a coupling transformer having an antenna winding connected with the said antenna and a circuit winding connected with the said terminal circuit and a thermionic -device having a cathode individual' emlssion and means for negatively biasing i each ofthe said grids with respect to the nearer cathode to prevent the flow of space current vbetween `the said cathodes Vwhen the voltage across the said antenna winding is less than a certain critical value.

In testimony whereof, I have signed my name to this specification this 27th day of December, 1922. I

WILLIAM H. T. HOLDEN. 

